Antenna



July 5, 1949. J. W.'MARCHETTI ANTENNA 2 Sheets- Sheet 1 Filed July 20, 1944 "IN V EN TOR. JOHN W. MARCHETTI ATTORNEY July 5, 1949. J. w. MARCHETTI ANTENNA 2 Sheets-Sheet 2 Filed July 20, 1944 ATTORNEY Patented July 5, 1949 umir o STATES TENT OFFICE ANTENNA Application July 20, 1944, Serial No. 545,799

(Granted under the act of March 3, 1883, as amended April" 30, 1928; 3'70 0. G. 757) 4' Claims.

The invention described. herein may be manufactured' and used by or for the Government for governmental. purposes,. without the payment to me of any royalty thereon.

My present invention relates to antennas, and more particularly, to an antennafor apulse-echo radio system for object-detection.-

In systems of the general: character indicated, especially those designed. for early warning, it is necessary that. the angle of. radiation of. the transmitted energy be kept low. Existing antennas capable of satisfying, this requirementhave done so only at the, sacrifice of higher angle coverage, and the undesirable. creation of gapsor null zonesdue to ground reflection.

It is therefore the main object of. my present invention to provide. anantenna, particularly, but not exclusively, for an early-warning, object-detecting radio system, whichovercomes the abovedescribed disadvantages,v and enables adequate. coverage throughout a relatively large elevational angle commencing substantially at the horizontal.

It is a further object of. my present invention to provide an antenna,.having.theforegoing-high ly desirable characteristics, which is simple in construction, easy and economical to. fabricate and assemble, and adapted to performitsintended functions in an. eflicient. manner.

These, and other objects andladvantages of my present invention, which will be better. understood as the detailed description thereof pr.o-- gresses, are attained, broadly, in the following manner:

I provide an antenna consisting. of a radiating head, and a parabolicreflector. The head. preferably includes aplurality ofhorizontally-polarized, half-wave dipole elements vertically stacked.

in the focal plane of the parabola.

The-radiating elements are so fed that, at the will of the operator, the parabola can be subjected to phase or anti-phase illumination. If the former, maximum energy. is. concentrated at and reflected from the center of the parabola, with a tapering oiT toward the outer periphery, and minor concentrations intermediate thecenter and the upper and lower regions of the reflecting surface. If the latter, there are two maxima of energy out of phase with each other, one occurring near each of the upper and lower regions of the reflecting surface, with minor concentrations on each side of saidmanim'a; and -a; minimum at the center.

With phase illumination, most of the energy is at a low angle and brokenup into approximately equalenergy zones. Withxanti-phase illumination, most of the energy zones are at higher angles with maximum and minimum zones which 2 dovetail with the maxima and minima of phase illumination.

In the accompanying specification there is described, and in the annexed drawings shown, what is at present considered a preferred. embodiment of the antennas of my present invention. It is; however, to be clearly understood that my present invention is not limited to said embodiment, inasmuch as changes therein may be made without the exercise of invention and within the true spirit and scope of the claims hereto appended.

In said drawings, Figure 1 is a fragmentary, partial front elevation, partial transverse section of an antenna made in accordance with the principles of my present invention;

Figure 2 is a perspective view of the radiating head thereof; and

Figure 3 is an example of the vertical coverage patterns obtainedwith my present invention, utilizing the aforementioned phase and anti-phase illumination.

Referring now more in detail to the aforesaid preferred embodiment of my present invention, with particular reference to Figures 1 and 2' of the drawings, the numeral 5 generally designates an antenna, comprising a radiating head i centrally disposed in the focal plane of a parabolic reflector 6.

The head 1 preferably includes three vertically stacked, horizontally-polarized, half-wave radiating dipoles 8, 9, and I0, and three similarly disposed and polarized parasitic reflecting elements ll, l2, and I3, located at an appropriate distancein advance of said radiating dipoles to prevent direct radiation from said dipoles in the forward direction.

Each of said radiating dipoles and each of said reflecting elements includes a pair of oppositely directed quarter-wavemembers M, the members of each of said pairs extending outwardly from;

outer conductors l5, I6, and H of coaxial trans-- mission lines I8, l9, and 20,

The outer conductors ofv said transmission lines on which is mounted a switching blade '21. The pivot is rotatably carried in the split end of an inner conductor 28 of a main coaxial transmission line 29 adapted to convey radio-frequency energy from a transmitter (not shown) to the radiating head 1, the outer conductor 30 of said transmission line being connected, directly, to the outer conductor [6, and being connected to the outer conductors l5 and I1, respectively, through sections 3| and 32.

The pivot 26 and the blade 21 carried thereby are adapted to be rotated through 90 by a small reversible electric motor 33 fed through a cable 34, the arrangement being such that, in one position of the blade 21, energy is simultaneously conveyed to the dipoles 8 and I0, and in the other position of said blade, energy is conveyed only to the dipole 9. The position of the blade is intended to be under the control of the operator of the aforementioned detecting system.

It will be noted that when the dipole 9 is energized, all of the energy illuminating the parabola 6 is in-phase, but when the dipoles 8 and I 0 are energized, because of the opposite connections, through the elements 25, of the inner conductors 22 and 24 t the quarter-wave members I4 of said dipoles 8 and [0, the parabola is subjected to anti-phase illumination.

Now, in Figure 3 of the drawings, I have shown, in full lines, the coverage patterns of the energy lobes (for radiation at 600 megacycles) which exist when the switch blade 21 is in such position that the parabola 6 is subjected to phase illumination, and I have also shown, in broken lines, the coverage patterns of the energy lobes obtained when the switch is in a position to subject the parabola to anti-phase illumination. It will be noted that the main lobe obtained with phase illumination is disposed at a very low angle from the horizontal, in the neighborhood of 2, while the minor lobe is disposed at an angle of about 6. Higher angle coverage is completely lacking, and there is a null zone of considerable extent between the major and minor lobes. However, when anti-phase illumination is resorted to, a greater total number of energy lobes is obtained, covering the region of space intermediate about 4 from the horizontal and about from the horizontal, with said lobes filling the null zones present when phase illumination is used.

It will thus be noted that by means of the present invention, I am able to eliminate the disadvantages associated With antennas heretofore designed for early-Warning object-detecting systems. namely, the lack of higher angle coverage, and the existence of extensive null zones within the region of space intended to be covered by the system. It will further be noted that by means of my present invention I am able to obtain adequate coverage throughout an elevational angle of considerable extent, commencing not much above the horizontal; and that the means employed to attain this highly desirable result are simple in construction, and easy to manufacture and use.

Other objects and advantages of my present invention will readily occur to those skilled in the art to which the same relates.

I claim:

1. An antenna comprising, in combination: a parabolic reflector; a plurality of radiating dipoles disposed in the focal plane of said reflector; a branched, coaxial transmission line for feeding at least two of said dipoles in opposite phase, and at least one other dipole in the same phase as that of either one of said oppositely phased dipoles; the outer conductors of the branches of said transmission line being slotted to determine the impedance presented to the points at which the elements of each of said dipoles are connected; and switching means for so connecting the branches of said transmission line to a source of radio-frequency energy that, at the will of the operator, said reflector may be subjected to phase or anti-phase illumination.

2. An antenna comprising, in combination: a parabolic reflector; a plurality of radiating dipoles disposed in the focal plane of said reflector; a branched, coaxial transmission line for feeding at least two of said dipoles in opposite phase, and at least one other dipole in the same phase as that of either one of said oppositely phased dipoles; the outer conductors of the branches of said transmission line being slotted to determine the impedance presented to the points at which the elements of each of said dipoles are connected; and motor-driven, mechanical switching means for so connecting the branches of said transmission line to a source of radiofrequency energy that, at the will of the operator, said reflector may be subjected to phase or anti-phase illumination.

3. In an early warning radar system, an antenna arrangement adapted to provide a wide, continuous vertical angle coverage beginning from a relatively low angle, said antenna arrangement comprising a single parabolic reflector, a first radiating dipole located at the intersection of the axis and the focal plane of said reflector, second and third radiating dipoles located in said focal plane on opposite sides of said axis, a branched coaxial transmission line for feeding said second and third dipoles in opposite phase and for feeding said first dipole in the same phase as that of either one of said second or third dipoles; the outer conductors of the branches of said transmission line being slotted to determine the impedance presented to the points at which the elements of each of said dipoles are connected, a source of radio energy, and switching means for so connecting the branches of said transmission line to said source of radio energy that alternatively either said first radiating dipole is energized or said second and third radiating dipoles are simultaneously energized.

4. The antenna arrangement set forth in claim 3, including a parasitic reflecting dipole disposed in advance of each of said dipoles to prevent direct radiation from said dipoles in a forward direction.

J OHN W. MARCHETTI.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,156,653 Ilberg May 2, 1939 2,187,618 Gerhard Jan. 16, 1940 2,234,293 Usselman Mar. 11, 1941 2,307,184 Alford Jan. 5, 1943 2,379,442 Kandoian July 3, 1945 FOREIGN PATENTS Number Country Date 706,661 Germany Apr. 30, 1941 

